New material of Schizopholis (family Botsfordiidae) from the Tsinghsutung Formation (Cambrian Series 2, Stage 4) in Songtao County, Guizhou Province, South China

Abstract. Organophosphatic brachiopods, widely distributed across several Cambrian tectonic plates, are crucial in understanding the evolution of early brachiopods. Here, we report newly discovered material of Schizopholis yorkensis from the Tsinghsutung Formation (Cambrian Series 2, Stage 4) in Songtao County, Guizhou Province, South China. This study presents the first systematic description of S. yorkensis from South China and extends its palaeobiogeographical distribution significantly. These specimens obtained through acid etching exhibit well-preserved morphological characteristics, including two tubercles on the dorsal metamorphic shell and three tubercles on the ventral metamorphic shell. Additionally, the ventral valve has divergent delthyrium throughout its ontogeny. Palaeogeographical analysis indicates that Schizopholis was predominantly distributed in low-latitude regions and reached its highest diversity level during the Cambrian Age 4, suggesting a phase of rapid spatial expansion during this interval. Schizopholis yorkensis was previously known from only North China and Australia during the Cambrian Age 3, but its subsequent distribution implies an expansion to South China and Antarctica during the Cambrian Age 4. In contrast, S. napuru is largely restricted to the Cambrian Age 4, providing vital auxiliary information for the palaeobiogeographical and biostratigraphical correlations.